GB 2186836 describes an extrusion die for producing an internally supported hollow article. The die comprises an outer die part having a single aperture therein and an inner die part comprising a plurality of fluid injectors permanently fixed to a manifold. A material is extruded around the injectors and through the single aperture such that the extrudate has a number of passages therein. GB 2186836 discloses two types of extrusion die which have different arrangements of injectors in the inner die part and different shapes of aperture in the outer die part. The two extrusion dies have been specially designed to produce particular extruded products and cannot be adapted to vary the external shape or the arrangement of passages in the extrudate.